Conventional frequency synthesizers accomplish the generation of many different frequencies from one or more stable sources by means of analog circuits or by a combination of analog and digital circuits. In these approaches, the generation of frequencies is performed in the analog or continuous sense by division, phase lock, mixing, or some combination of these techniques.
A numerically controlled oscillator (NCO) generates a sinusoidal wave form whose frequency is digitally controlled. The greatly increased demand for a high speed, low power NCO derives directly from two clear trends in communication technology: (1) the rapidly expanding role of digital techniques and processing; and (2) the increasing emphasis upon precise frequency control. Although the speed, power, and size considerations dictate integrated circuit NCO implementation, previously available design and processing techniques have been inadequate to satisfactorily resolve the conflict between stringent performance requirements and the limitations of practical technology. Prior art NCO's were formed on a plurality of semiconductor chips, generally at least a read-only-memory is external to the main NCO chip, which greatly increased the space and amount of power required.